Hey Sculley,
my apologies for the delay in my reply!
The slider images are indeed 960×330 px. As far as I can see from your website, the image (the one with stacked rocks) you are currently using in the slider is 2048×1536 px, which would translate, without losing the aspect ratio, to 960×720 px (retaining the width) or 440×330 px (retaining the height). Please use an image for the slider which is 960×330 px or is proportional to these dimensions (e.g. 1920x660px).
Sincerely,
Andrii / Satori Studio